The present invention relates to a photolithographic patterning material and a method for the formation of a fine pattern by using the same. More particularly, the invention relates to a multilayered photolithographic patterning material and a photolithographic method for the formation of a fine pattern therewith by utilizing a near-field light.
As is known, the photolithographic fine patterning is a well established and widely practiced technology in the manufacture of a great variety of electric and electronic parts including semiconductor silicon-based LSIs and originals of optical disks. It is a requirement in this field of technology to accomplish more and more increased fineness of patterning in order to comply with the rapid increase in the quantity of accumulated information recording and in the information-processing quantity.
The photolithographic patterning process currently undertaken is conducted by exposing a photosensitive resist layer formed on a substrate with active rays through a pattern-bearing photomask to form a latent image of the pattern which is then developed by using a developer solution. A factor limiting the minimum dimension of the thus formed resist pattern is diffraction of the light so that the minimum dimension actually accomplished in practice can be only slightly smaller than the wavelength of the light used in the pattern-wise exposure of the photoresist layer. Needless to say, the diffraction limit depends on the wavelength of the light and the numerical aperture of the lens system used for the light exposure and the limit value can be decreased as the wavelength of the light is decreased and as the numerical aperture of the lens system is increased. Since it is technologically an extremely difficult matter to design a lens system having a numerical aperture exceeding the value of current lens systems, the development works to accomplish further increased fineness of photolithographic patterning are exclusively directed to the utilization of light having a shorter and shorter wavelength.
Accordingly, intensive investigations are now under way to develop a novel patterning exposure technology by employing deep ultraviolet light, electron beams, laser beams, soft X-rays and the like. Needless to say, the technology for obtaining a line-and-space patterned photoresist layer having a line width of 100 nm or finer cannot be accomplished without solving various peripheral problems such as development of high-performance light sources and improvement in the performance of the optical materials and photoresist compositions.
On the other hand, an alternative approach to this problem is now receiving attention for accomplishing photolithographic patterning of a photoresist layer with fineness not attained by the conventional methods utilizing a near-field light which is inherently free from the limitation of light diffraction. For example, a method is proposed that a near-field probe having a microaperture of several tens of nanometers is provided at the sharpened end point of an optical fiber and the near-field probe is brought near to the surface of a photoresist layer on which a pattern is drawn by the near-field light going to the microaperture through the optical fiber (see Japanese Patent Kokai 7-106229, 8-248641 and 10-326742).
In this method, however, the surface of the photoresist layer must be scanned over a substantial area with the near-field probe under control of the near-field probe at a distance of only several tens of nanometers from the surface of the photoresist layer taking a long time for scanning. Since this scanning is performed by using a stage having a large number of piezoelectric elements with a few nanometer resolution, moreover, the range which can be patterned at one time is limited to be several micrometers to several tens of micrometers so that wide-range writing is practically impossible and, in addition, the photosensitive material must have a particularly high photosensitivity due to the low utilization efficiency of light in the microaperture.
A further proposal is made in Japanese Patent Kokai 8-179493 for a method in which a photomask bearing a fine pattern is laminated onto the surface of the photosensitive material either directly or with intervention of a gap layer to be exposed to the near-field light. This method, however, has a problem that, when pattern-wise exposure is desired over a wide area by this method, the pattern-bearing photomask must be a large size one while such a large fine mask pattern can be prepared practically only with a great difficulty by imaging with electron beams over a wide area.
Besides, a method is disclosed in Japanese Patent Kokai 9-7935 in which a thin film of a non-linear optical material or, namely, a thin film of which the light transmittance is increased with the intensity of the incident light is brought into direct contact with the photoresist layer and the thin film is irradiated spotwise with light so as to effect a local increase in the light transmittance of the thin film forming a desired pattern in the thin film by the relative scanning of the light spot and the photoresist layer, through which the photoresist layer is pattern-wise exposed to light. By undertaking this method, it is possible to conduct direct imaging of a fine pattern below the diffraction limit with a laser beam and patterning at a high speed with a near-field light.
In this method, however, the thin film of a non-linear optical material is in direct contact with the photoresist layer so that the numerical aperture and the distance from the surface of the photoresist layer, each as a parameter determinant of the resolution with the near-field light, cannot be controlled not to give an option for the selection of the optimum exposure conditions for the near-field light. In addition, the light-induced changes in the non-linear optical material are irreversible so that multiple exposure or repeated exposure cannot be undertaken by using a single pattern-bearing photomask.
The present invention accordingly has an object, in order to overcome the above described problems and defects in the conventional photolithographic fine patterning methods by utilizing a near-field light, to provide a photolithographic patterning material suitable for the formation of a fine resist pattern over a wide area with a greatly increased speed and capable of being used repeatedly as well as to provide a method for photolithographic fine patterning of the resist layer by utilizing the patterning material.
Thus, the photolithographic patterning material provided by the present invention is a multilayered integral body which comprises:
(a) a substrate;
(b) a photosensitive resist layer formed on one surface of the substrate; and
(c) a composite layer for generation of a near-field light, which is formed on the photoresist layer, consisting of
(c1) a first dielectric layer of a dielectric material in direct contact with the photoresist layer,
(c2) a layer of a non-linear optical material, and
(c3) a second dielectric layer of a dielectric material, the layer (c2) being sandwiched between the first dielectric layer (c1) and the second dielectric layer (c3).
Preferably, the first dielectric layer (c1) intervening between the photoresist layer (b) and the layer (c2) has a thickness not exceeding 150 nm and the layer (c2) of the non-linear optical material has a thickness in the range from 5 nm to 200 nm.
The method of the invention for photolithographic fine patterning of a photoresist layer by using the above defined photolithographic patterning material comprises the step of: exposing pattern-wise the photosensitive resist layer (b) to active rays through the composite layer (c) for generation of a near-field light.
In this method, in particular, the active rays are focused to the layer (c2) of a non-linear optical material to form an opening or a microspot of light scattering in which a near-field light is generated for image-forming exposure of the photoresist layer.